This invention relates to water treatment processes and more particularly to the treatment of alkaline aqueous solutions used in secondary petroleum recovery processes.
In the recovery of petroleum from subterranean reservoirs it is usually advantageous to employ a driving fluid to enhance the displacement of the reservoir petroleum and to move it toward one or more production wells for subsequent recovery and processing. These displacement fluids are normally comprised, wholly or in part, of water, typically water produced from or readily available at the well site. It is also highly desirable that the pH of the displacement fluid be maintained on the alkaline side so that the interfacial tension between the reservoir oil and the displacement fluid is reduced and the displacement efficiency is substantially improved.
The water most readily available for use as the displacement fluid or injection water normally has a substantially high concentration of total dissolved salts, particularly magnesium and calcium salts. A serious problem with any hard water, and particularly with injection water, is that insoluble precipitates are formed which rapidly deposit as scale on pump parts and within the pipelines. The formation of these deposits, which is referred to as scaling, requires periodic acid washing to remove the deposits. Failure to properly remove the deposits can result in the malfunctioning and the shortening of the useful life of the components of a water-handling system, such as the pumps and lines.
Needless to say, in many situations the water can be softened or demineralized in order to remove the insoluble precipitate precursors and thus largely eliminate the scaling problem. In the case of the handling or treatment of large volumes of water, however, such as is encountered in connection with petroleum recovery processes and the like, the volume of water renders conventional softening or demineralization processes uneconomical. There is also a problem of the disposal of the brine liquors or precipitates which are normally produced in the course of conventional water-treatment processes. In addition many of the salts present in the water to be used in oil recovery processes, such as sodium chloride, are beneficial to the process and their removal along with the scale forming precursors would not be desirable.
Consequently, it would be highly advantageous to provide a process in which alkaline aqueous solutions are treated to reduce their scaling tendencies and the waste product of the treatment process placed in a form for underground disposal. Additionally, it would be highly advantageous to provide a process for the treatment of water to reduce its scaling tendencies which process can be utilized in conjunction with a caustic flooding process in which precipitated solids are redissolved and utilized to control the mobility of the displacement fluid in the reservoir.